It is known that both agglomerate and natural stone materials present a certain rigidity; these materials can be used to obtain sheets or panels of a limited length and with a not excessively reduced thickness since a not perfect placing could induce cracks with consequent breakage.
For the above reasons, the thicknesses obtained must not fall below predetermined minimum values in order to prevent inevitable problems due to the rigidity of the materials.
The dimensional tolerances, relative to length, width and thickness, that can arise in the production of a traditional sheet are unfavourably high, which means that the sheets obtained can greatly differ one from the next obvious problems at the time of their use.
The background art includes a process for the production of panels or sheets made from agglomerate material consisting of for example quartz and sand and intrusions of various types (metal, glass, ceramic, wood, precious stones, etc.), or of granite, quartz or sand together with predetermined quantities of resin binders.
This process includes various processing stages, i.e.:                an initial stage in which the various materials which make up the agglomerate are crushed;        a second stage in which the crushed materials are mixed, in order to obtain a product which is as homogeneous as possible, during which the resin binders are added;        a third stage in which the agglomerate is pressed and compacted, during which the desired shape is obtained;        a fourth stage in which the panel is hardened at a predetermined temperature;        a fifth stage in which the two sides of the panel are smoothed and hardened;        a sixth stage in which the panel is cut to size, chamfered, calibrated and reamed, followed by discharge of the end products.        
A procedure such as the one described above makes it possible to obtain panels or sheets made from agglomerate material with carefully predetermined lengths, widths and thicknesses, and can be carried out on a continuous basis by an appropriate plant.
A distributor or spreader is positioned between the second mixing stage and the third pressing and compacting stage to transfer the crushed material in special moulds in order to give the material a predetermined configuration before the subsequent vibration compression.
One drawback is represented by the fact that the distribution of the crushed material inside the said moulds does not always take place in an uniform way, and the presence of any fragments with a pronounced degree of granulometry can cause the formation of permanent cavities or holes in the finished product.
Document EP-A-786325 describes a method and apparatus for the production of granulated stone materials and/or sands bound with a hardenable resin. According to said method a mixture of granulated stone material and/or sand with a hardnable resins is spread on a support so as to form a layer of uniform thinkness, whereby the support is previously protected by a sheet material, and the layer in question, which is also protected on its upper surface by a similar sheet material, undergoes a vibratory compaction under vacuum and a hot hardening process.
Said method is rather complicated and economically not favourable since the application of the sheet material as lower support and upper protection can be improperly paired with negative effect during the vibration stage or the application of the vacuum.